1. Field of the Invention
The present invention is directed to projection systems, and more particularly to a method and apparatus for monitoring the condition of a projector lamp.
2. Description of the Related Art
Digital projection systems are well known in the art, having been used for many years in diverse applications, including the film industry, military and civilian simulations, control rooms, etc.
High-end projector systems typically use Xenon arc lamps coupled to an ellipsoid reflector. The reflected light is captured from a first focal point of the reflector and is re-imaged at a second focal point. The second focal point is commonly co-incident with an optical component such as an integrator rod, projector lens, etc., depending on the implementation.
Xenon arc lamps are expensive and subject to performance degradation over time. More particularly, when such lamps are used over a long time, the material contained in the lamp electrodes gradually vaporizes and is deposited on the wall surface of the inside of the lamp bulb—a condition referred to in the art as “blackening.” During lamp operation, the blackened portion absorbs heat and light energy from the lamp's arc such that continued lamp operation in the presence of blackening results in a persistent temperature increase and lower luminous output.
Tolerances of lamp components and manufacturing craftsmanship are such that every lamp exhibits unique thermal and luminous performance characteristics relative to its lamp lifetime. Therefore, predicting lamp luminous output as a function of lamp operating life can be difficult. It is known in the art to use profile graphs to characterize the luminous output degradation of a ‘typical lamp’. However, projection lamps are often operated under varied conditions that are not covered by the lamp profile graph of a ‘typical’ lamp and in many instances the lamp graph is either not known or not supplied by the manufacturer.
What is needed therefore is a way to monitor one or more properties of each individual lamp such that its condition can be known. One property that may be exploited with this goal in mind is the build-up of evaporated materials on the inner envelope of the lamp bulb (i.e. blackening).
U.S. Pat. No. 6,365,899 discloses a process for determination of lamp blackening based on the difference between the spectral radiant energy emitted by the lamp bulb when blackening occurs as compared to when blackening does not occur. Specifically, the amount of increase in radiant energy emitted by the bulb is detected in use relative to when the lamp was first turned on. Thus the method according to U.S. Pat. No. 6,365,899 relies on the change in radiated energy from the lamp itself to determine the degree of bulb blackening. This requires careful selection of the bandpass filters that are tailored for certain lamp types (Xenon, metal halide, high pressure mercury, UHP and others), which can cause interference with the lamp's strong emission lines resulting in system unreliability.